An internal combustion engine is conventionally equipped with an exhaust line, for leading the exhaust gas from the engine to the environment, and with a plurality of after treatment devices located in the exhaust line, for degrading and/or removing pollutants from the exhaust gas. More particularly, the after treatment devices of a Diesel engine usually comprise a Diesel Oxidation Catalyst (DOC), for oxidizing hydrocarbon (HC) and carbon monoxides (CO) into carbon dioxide (CO2) and water (H2O), and a Diesel Particulate Filter (DPF), located in the exhaust line downstream the DOC, for removing diesel particulate matter or soot from the exhaust gas.
In order to reduce NOx emissions, most Diesel engine further comprise an SCR catalyst, which is located in the exhaust line downstream the DPF, in order to promote a Selective Catalytic Reduction (SCR) of the nitrogen oxides (NOx) contained in the exhaust gas. As a matter of fact, the SCR catalyst is a catalytic device in which the nitrogen oxides (NOx) contained in the exhaust gas are converted into diatomic nitrogen (N2) and water (H2O), with the aid of a gaseous reducing agent, typically ammonia (NH3), which is stored inside the catalyst. The ammonia is obtained through thermo-hydrolysis of a Diesel Exhaust Fluid (DEF), typically urea (CH4N2O) that is injected into the exhaust line by means of a dedicated injector located between the DPF and the SCR catalyst.
The DEF injector is controlled by an engine control unit (ECU), which regulates the DEF quantity to be injected, such as to obtain a satisfactory NOx conversion rate inside the SCR catalyst. As a matter of fact, the ECU determines the DEF quantity to be injected with a control procedure which generally requires for determining many physical parameters of the exhaust gas flowing in the exhaust line, such as for example the exhaust gas temperature upstream the SCR catalyst, the exhaust gas temperature downstream the SCR catalyst, the concentration of NOx upstream the SCR catalyst and the NOx concentration downstream the SCR catalyst.
Conventionally, these parameters are measured by means of dedicated sensors connected to the ECU, including a first temperature sensor located in the exhaust line between the DPF and the SCR catalyst, a second temperature sensor located in the exhaust line downstream the SCR catalyst, a first NOx sensor located in the exhaust line between the DPF and the SCR catalyst, and a second NOx sensor located in the exhaust line downstream the SCR catalyst. A drawback of this solution is that the use of so many sensors complicates the architecture of the exhaust line and increases the cost of the same.
In view of the foregoing, it is at least one object to reduce the number of sensors in an internal combustion engine, thereby solving, or at least positively reducing, the above mentioned drawback. At least another object is to reduce the number of sensors involved in the control procedure of the SCR catalyst, as well as in any other control procedure which requires for determining both the temperature and the NOx content of the exhaust gas. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.